Research On Non-contact Post-arc Current Measurement Based On TMR Sensor

The continuous expansion of the high-voltage circuit breakers’s application in power systems has put forward higher requirements for its breaking time,opening stability,and service life.The post-arc current is an important evaluation index in the research of high-voltage circuit breakers,which can reflect the post-arc characteristics such as the transient recovery voltage intensity,post-arc conductance and post-arc charge of the high-voltage circuit breaker in the breaking process.The post-arc current measurement methods are all contact measurements,including shunts,transfer resistors,diode clamps,etc.These methods have strict requirements on the opening time of the circuit breaker,the selection of resistors and diodes,which are easy to damage the measuring components and cause high-voltage safety hazards.Different from contact measurements,the non-contact post-arc current measurement based on the TMR sensor can realize the measurement without connecting to the breaker circuit.This paper firstly expounds the theoretical research of current measurement based on magnetic sensor,compares and analyzes the advantages and disadvantages of TMR sensor,Hall sensor,AMR sensor and GMR sensor,points out the advantages of TMR sensor in post-arc current measurement.According to the measurement principle of TMR sensor,the mathematical model of current and output voltage is established,and the black-box model of current is proposed.A measurement system based on TMR sensor is designed,including power module,operational amplifier module and sensor module,the design and performance simulation of electromagnetic shielding device are carried out in Maxwell.Secondly,in order to study the performance indicators of the TMR measurement system,the DC current and AC current tests were carried out in turn,and the theoretical current was obtained according to the deduced current mathematical model,and the relative error between the theoretical current and the measured current was calculated.The DC test results show that the forward and reverse directions of the current have no effect on the measurement results,and the relative error of the current is within 4%.Comparing the test results at different distances,it is found that the closer the sensor is to the current,the greater the sensor output voltage.The AC test results show that the relative error of the current is within 5%,and the minimum current that can be measured is 90m A.The above test results provide a test basis for the measurement of the post-arc current.Finally,the post-arc current simulation and test were carried out,and the post-arc current was simulated and analyzed in the ATP-EMTP software.The simulation results showed that the post-arc current peak value was A,and the duration wasμs;the transient recovery voltage would affect the post-arc current.Within a certain range,the greater the peak value of transient recovery voltage,the greater the peak value of post-arc current.A post-arc current test platform was built.The test circuit breaker was a C₄F₇N-CO₂ mixed gas circuit breaker with a breaking current of 1.25 k A.The post-arc current was measured under the transient recovery voltage of 2k V to 4k V in turn,with a peak value of 1.98A to 4.84A.After the loop current crosses zero,the post-arc current rapidly increases to the peak value and then decreases gradually under the impact of the transient recovery voltage,and finally tends to zero.The whole process lasts within 100μs.Compared with the results of post-arc current measured by predecessors,the validity of this measurement system is verified.